Image sensor units have been used as image reading apparatuses for use in, e.g., a facsimile, a copying machine, and a scanner. Among the image sensor units, a contact image sensor unit (CIS: Contact Image Sensor) is known as an image sensor unit using a rod lens array. The contact image sensor unit structurally requires a rod lens array of a length equal to the reading width of the contact image sensor. In the design of a long (or short), image sensor, use of a rod lens array of a length tailored to the reading width of the image sensor is necessary. This leads to the need for preparation of a specialized part and increased cost.
For example, Patent Document 1 proposes an image sensor unit which realizes formation of a long rod lens array 30 using general-purpose rod lens arrays by connecting (joining) rod lens arrays 30A and 30B of a fixed length to each other, in the design of a long image sensor as illustrated in FIG. 12.
Patent Document 1: Japanese Laid-open Patent Publication No. 2005-217630